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A discussion on channel sensing techniques By James Xu Supervised by Dr. Fakhrul Alam
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Presentation overview Introduction to wireless communications What is Cognitive Radio (CR)? Why do we need CR? What is channel sensing Our workbench setup Our research Our major contributions Conclusion
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Wireless communications
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What is Cognitive Radio (CR) Able to sense spectral environment Able to provide opportunistic access Find gaps in the spectrum Adjust system parameters to utilize it
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Why do we need CR? Unlicensed spectrum is rare Almost none available under 3GHz
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Why do we need CR? Licensed to primary user only (Incumbent) We are running out of space, and higher frequency has problems We are under utilizing licensed space CR is allowed usage (guarantee interference free)
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What is channel sensing The first step of CR is to identify free spectrum Channel sensing is one of the most fundamental part of CR
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What is channel sensing
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Our research Our research focus Energy detection Cyclostationary feature extraction
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Our CR workbench
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Energy detection Easy to implement Fast Not effective under low SNR
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What is energy detection? All radio transmission have energy Based on hypothesis testing
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Energy detector
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Problems with the detector Misdetection on Narrowband signals
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Problems with the detector Misdetection on partial signals
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Adaptive energy detection We proposed an improvement Introduced adaptive detection
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Improved detection
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Adaptive ED characteristics
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Cyclostationary Features Another channel sensing strategy Digital communication systems have built in periodicity A signal is a first order cyclostationary if it’s mean is periodic A signal is second order cyclostationary it it’s auto-correlation is periodic
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Cyclostationary Features Auto-correlation how much a signal has in common with itself, against delay Alpha = Cyclic frequency S = Spectrum Correlation Function (SCF)
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Cyclostationary Features
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Work in Progress This is preliminary, a proof of concept Could be done in future research
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Our major contributions Xu J. Y., Alam, F., Adaptive Energy Detection for Cognitive Radio: An Experimental Study, ICCIT, 2009 IET PATW Competition, Regional winner cr.jamesyxu.com Svn://cr.jamesyxu.com/svn CRLibs
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CRLibs A library for cognitive radio research
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Conclusion Workbench setup Investigated various channel sensing techniques (ED, SCF, Spectral Entropy) Proposed and implemented improvements (AED) Consolidated library (CRLibs), examples and codebase (SVN) Full progress documentation (SVN, CR)
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Acknowledgement Dr Fakhrul Alam Dr James Chang Dr Tom Moir Everyone in our lab
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Thank you for listening You are invited to visit our CR workbench at Building 80 Much more details in the project report Adaptive energy detection model will be on IEEEXplore end of December Any questions?
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